Add histogram for safebrowsing download ping payload size.

chrome/browser/safe_browsing/download_protection_service.cc

Index: chrome/browser/safe_browsing/download_protection_service.cc
diff --git a/chrome/browser/safe_browsing/download_protection_service.cc b/chrome/browser/safe_browsing/download_protection_service.cc
index 6756bbf027a68a8830a9be91f6b2eb37923fde00..473dc5348dfdb212a1c46065a7802e2c29237a93 100644
--- a/chrome/browser/safe_browsing/download_protection_service.cc
+++ b/chrome/browser/safe_browsing/download_protection_service.cc
@@ -668,6 +668,8 @@ class DownloadProtectionService::CheckClientDownloadRequest
     fetcher_->SetRequestContext(service_->request_context_getter_.get());
     fetcher_->SetUploadData("application/octet-stream",
                             client_download_request_data_);
+    UMA_HISTOGRAM_COUNTS("SBClientDownload.DownloadRequestPayloadSize",
+                         client_download_request_data_.size());

[Ilya Sherman, 2013/07/30 01:27:39]

Are you sure that a histogram mapping [1, 1,000,000) bytes gives you the dynamic
range that you want?  It seems likely to me that you might not care so much
about distinguishing payload sizes on the order of 1-10 bytes, and possibly care
about distinguishing payload sizes on the order of 1-10 megabytes.  If so, you
might want to switch this histogram to measure KB instead of just bytes.

[mattm, 2013/07/30 01:53:23]

This is actually the size of the ping we send to the safebrowsing server, not
the size of the file we are checking, so it shouldn't be that big.

     fetcher_->Start();
   }